U.S. Pat. No. 3,652,589 discloses a class of analgesic cycloalkanol-substituted phenol esters having a basic amine group in the cycloalkyl ring. The compound (1R, 2R or 1S, 2S)-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)-cyclohexanol, commonly known as tramadol, is specifically disclosed therein. A series of articles pertaining to the pharmacology, toxicology and clinical studies of tramadol are found in Arzneim, Forsch. (Drug Res.), 28(I), 114 (1978). Driessen et al., Arch. Pharmacol., 341, R104 (1990) disclose that tramadol produces its analgesic effect through a mechanism that is neither fully opioid-like nor non-opioid-like. The Abstracts of the Vlth World Congress on Pain, Apr. 1-6 (1990), disclose that tramadol hydrochloride is an orally active pure agonist opioid analgesic. However, clinical experience indicates that tramadol lacks many of the typical side effects of opioid agonists, e.g., respiratory depression (W. Vogel et al., Arzneim Forsch. (Drug Res.), 28(I), 183 (1978)), constipation (I. Arend et al., Arzneim. Forsch. ( Drug Res.), 28(I), 199 (1978)), tolerance (L. Flohe et, al., Arzneim. Forsch. (Drug Res.), 28(I), 213 (1978)), and abuse liability ( T. Yanagita, Arzneim. Forsch. (Drug Res.), 28(I), 158 (1978)). When given at a dose of 50 mg by rapid i.v. injection, tramadol may produce certain side effects unique to tramadol including hot flushes and sweating. Despite these side effects, tramadol's combination of non-opioid and opioid activity makes tramadol a very unique drug. Tramadol is currently being marketed by Grunenthal GMBH as an analgesic.
Opioids have for many years been used as analgesics to treat severe pain. They, however, produce undesirable side effects and as a result cannot always be given repeatedly or at high doses. The side effect problems are well documented in the literature. See, for example, J. Jaffe in "Goodman and Gilman's, The Pharmacological Basis of Therapeutics", 8th edition; Gilman et al.; Pergamon Press, New York, 1990; Chapter 22; pages 522-573 wherein it is disclosed that morphine and its congeners, e.g., codeine, hydrocodone and oxycodone, are opioid agonist analgesics that exhibit side effects such as respiratory depression, constipation, tolerance and abuse liability.
As alternatives to using opioids, non-opioids such as acetaminophen, aspirin and ibuprofen are used as analgesics. Ibuprofen, like aspirin, is not subject to the tolerance, addiction and toxicity of the opioid analgesics. However, ibuprofen, aspirin and other nonsteroidal antiinflammatory drugs (commonly referred to as NSAIDs) are only useful in relieving pain of moderate intensity, whereas the opioid analgesics are useful in relieving more intense pain; See Woodbury, D. and Fingl, E. in "The Pharmacological Basis of Therapeutics", 5th Ed.; Goodman, L. and Gilman, A., Chapter 15, (1975).
To reduce the side effect problems of opioids, opioids have been combined with other drugs including non-opioid analgesic agents, which lower the amount of opioid needed to produce an equivalent degree of analgesia. It has been claimed that some of these combination products also have the advantage of producing a synergistic analgesic effect. For example, A. Takemori, Annals New York Acad. Sci., 281,262 (1976) discloses that compositions including combinations of opioid analgesics with drugs other than analgesics exhibit a variety of effects, i.e., subadditive (inhibitory), additive or superadditive. R. Taber et al., J. Pharm. Expt. Thera., 169(1), 29 (1969) disclose that the combination of morphine and methadone, another opioid analgesic, exhibits an additive effect. U.S. Pat. No. 4,571,400 discloses that the combination of dihydrocodeine, an opioid analgesic, and ibuprofen, a non-opioid analgesic, provides superadditive effects when the components are within certain ratios. See also U.S. Pat. Nos. 4,587,252 and 4,569,937 which disclose other ibuprofen opioid combinations. A. Pircio et al., Arch. Int. Pharmacodyn., 235, 116 (1978) report superadditive analgesia with a 1:125 mixture of butorphanol, another opioid analgesic, and acetaminophen, a non-opioid analgesic, whereas a 1:10 mixture did not show any statistically significant superadditive analgesia.
Combinations of non-opioid analgesics have also been prepared to avoid the side effects associated with opioids, and the combinations are noted to have the benefit of requiring less of each ingredient and producing superadditive effects. G. Stacher et. al., Int. J. Clin. Pharmacol. Biopharmacy, 17, 250 (1979) report that the combination of non-opioid analgesics, i.e., tolmetin (another NSAID) and acetaminophen, allows for a marked reduction in the amount of tolmetin required to produce analgesia. In addition, U.S. Pat. No. 4,260,629 discloses that an orally administered composition of acetaminophen and zomepirac, a non-opioid analgesic, in a particular weight ratio range produces a superadditive relief of pain in mammals. Furthermore, U.S. Pat. No. 4,132,788 discloses that 5-aroyl-1-(lower)alkylpyrrole-2-acetic acid derivatives, non-opioid analgesics, when combined with acetaminophen or aspirin exhibit superadditive antiarthritic activity. However, there have been warnings against the daily consumption of non-opioid analgesic mixtures and of the consumption of a single non-opioid analgesic in large amounts or over long periods (see, D. Woodbury and E. Fingl at page 349). In addition, ibuprofen, aspirin and some other NSAIDs may cause gastrointestinal side effects especially if used repeatedly. See, for example, M. J. S. Langman, Am. J. Med. 84 (Suppl. 2A): 15-19, 1988; P. A. Insel in "The Pharmacological Basis of Therapeutics" 8th Ed.; Gilman, A.G. et al., Chapter 26, pp. 664-668, 1990.
The prior art, however, does not disclose that tramadol, an `atypical` opioid analgesic, can or should be combined with another analgesic to lessen the side effects of each or to yield a composition comprising a tramadol material and another analgesic that exhibits superadditive analgesia.